Dimensionally stable polyester yarn for high tenacity treated cords

ABSTRACT

Polyethylene terephthalate yarn is prepared by spinning under high stress conditions in the transition region between oriented-amorphous and oriented-crystalline undrawn yarns by selection of process parameters to form an undrawn yarn that is a crystalline, partially oriented yarn with a crystallinity of 3 to 15 percent and a melting point elevation of 2 to 10° C. The spun yarn is then hot drawn to a total draw ratio between 1.5/1 and 2.5/1 with the resulting properties: (A) a terminal modulus of at least 20 g/d, (B) a dimensional stability defined by E 4.5 +FS&lt;13.5 percent, (C) a tenacity of at least 7 grams per denier, (D) a melting point elevation of 9 to 14° C., and (E) an amorphous orientation function of less than 0.75. The resulting treated tire cord provides high tenacity in combination with improved dimensional stability.

[0001] This is a continuation-in-part application of copending U.S.application Ser. No. 215,178 filed Jul. 5, 1988.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to polyester multifilament yarn with highmodulus and low shrinkage particularly useful for the textilereinforcement of tires. The yarn of the invention provides high treatedcord tenacity while maintaining or increasing treated cord dimensionalstability when compared to prior art yarns. A process for production ofthe multifilament polyester yarn is an aspect of the invention.

[0004] 2. Description of the Prior Art

[0005] Polyethylene terephthalate filaments of high strength are wellknown in the art and are commonly utilized in industrial applicationsincluding tire cord for rubber reinforcement, conveyor belts, seatbelts, V-belts and hosing.

[0006] Continued improvement in high strength industrial yarnsparticularly suited for use as fibrous reinforcement in rubber tires isan ongoing need in the industry. In particular, the improvement oftreated cord tenacity and dimensional stability are desired objectives.U.S. Pat. No. 4,101,525 to Davis et al. provides an industrial strengthmultifilament polyester yarn with high initial modulus and lowshrinkage. Although Davis et al. does not provide treated cord data, itis commonly known that compared to conventional tire cords such yarnprovides a reduced tenacity when the yarn is converted to the treatedtire cord. Additionally, rapid cooling of the filament immediately afteremerging from the spinneret can result in excessive filament breakageand thus yield yarn with poor mechanical quality. U.S. Pat. No.4,491,657 to Saito et al. discloses high modulus, low shrinkagepolyester yarn, but requires a low terminal modulus to achieve good yarnto treated cord conversion efficiency for such dimensionally stableyarns. The low terminal modulus is carried over into the treated cordand results in a lower tenacity than the high terminal modulus cords ofthe present invention. Also, as shown in FIG. 8 the process of Saito etal. requires high spinning speeds, which makes it difficult to processon-panel, i.e. a continuous spin-draw process.

SUMMARY OF THE INVENTION

[0007] Polyethylene terephthalate yarn can be prepared by spinning underhigh stress conditions in the transition region betweenoriented-amorphous and oriented-crystalline undrawn yarns. The inventionis accomplished by selection of process parameters to form an undrawnyarn that is a crystalline, partially oriented yarn with a crystallinityof 3 to 15 percent and a melting point elevation of 2 to 10° C. The spunyarn is then hot drawn to a total draw ratio between 1.5/1 and 2.5/1with the resulting unique combination of properties: (A) a terminalmodulus of at least 20 g/d, (B) a dimensional stability defined byE_(4.5)+FS<13.5 percent, (C) a tenacity of at least 7 grams per denier,(D) a melting point elevation of 9 to 14° C., and (E) an amorphousorientation function of less than 0.75. The drawn yarn is twisted andplied to produce tire cord and then treated withresorcinol-formaldehyde-latex. The resulting treated tire cordunexpectedly provides high tenacity in combination with improveddimensional stability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 represents treated cord dimensional stability as judged byplots of LASE-5 versus free shrinkage for the yarns prepared in ExampleI.

[0009]FIG. 2 represents a comparison of treated cord tenacities at agiven free shrinkage for the yarns of Example I.

[0010]FIG. 3 represents treated cord dimensional stability as judged byplots of LASE-5 versus free shrinkage for the yarns prepared in ExampleII.

[0011]FIG. 4 represents a comparison of treated cord tenacities at agiven free shrinkage for the yarns of Example II.

[0012]FIG. 5 represents a plot of LASE-5 versus free shrinkage of drawnyarns from Example II.

[0013]FIG. 6 plots treated cord tenacity versus LASE-5 at a given freeshrinkage (4 percent) and demonstrates the unexpected increase intreated cord tenacity obtained by the yarns of this invention. (ExampleII

[0014]FIG. 7 represents the percent crystallinity and melting pointelevation for the undrawn yarns for Example II.

[0015]FIG. 8 gives the range of spinning speeds wherein prior art U.S.Pat. No. 4,491,657 teaches that different undrawn birefringences can beachieved.

[0016]FIG. 9 gives the DSC traces for drawn yarns from Example II.

[0017]FIG. 10 represents a plot of the shrinkage force vs. freeshrinkage of drawn yarns from Example II.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] The high strength polyester multifilament yarn of the presentinvention provides improved dimensional stability together with improvedtreated cord tenacity when incorporated as fibrous reinforcement intorubber composites such as tires.

[0019] With the current emphasis on the monoply radial passenger tire,the demand for ever increasing dimensionally stable cords continues tobe high. Dimensional stability is defined as high modulus at a givenshrinkage and directly relates to tire sidewall indentations (SWI) andtire handling. While the modulus of the cord in the tire is the primaryvariable governing both SWI and handling, shrinkage is important in twoways. First, excessive cord shrinkage during tire curing cansignificantly reduce the modulus from that of the starting treated cord.Second, cord shrinkage is a potential source of tire non-uniformity.Thus, comparison of modulus and tenacity at a given shrinkage is ameaningful comparison for tire cords. Since tire cords experiencedeformations of a few percent during service, a good practical measureof modulus is LASE-5 (load at 5 percent elongation). Alternatively,E_(4.5) (elongation at 4.5 g/d load) can be used as a practical measureof compliance.

[0020] For both tire SWI and handling, modulus at elevated temperature(up to 120° C.) is the ‘true’ parameter governing performance. Due tothe highly crystalline nature of treated cords based on conventional ordimensionally stable yarns, the modulus retention (in percent) atelevated tire temperatures is essentially similar for all currentcommercial treated cords and for those of this invention. Thus, roomtemperature measurement of LASE-5 is sufficient to establish meaningfuldifferences in cord dimensional stability.

[0021] The polyester yarn contains at least 90 mol percent polyethyleneterephthalate (PET). In a preferred embodiment, the polyester issubstantially all polyethylene terephthalate. Alternatively, thepolyester may incorporate as copolymer units minor amounts of unitsderived from one or more ester-forming ingredients other than ethyleneglycol and terephthalic acid or its derivatives. Illustrative examplesof other ester-forming ingredients which may be copolymerized with thepolyethylene terephthalate units include glycols such as diethyleneglycol, trimethylene glycol, tetramethylene glycol, hexamethyleneglycol, etc., and dicarboxylic acids such as isophthalic acid,hexahydroterephthalic acid, bibenzoic acid, adipic acid, sebacic acid,azelaic acid, etc.

[0022] The multifilament yarn of the present invention commonlypossesses a denier per filament of about 1 to 20(e.g. about 3 to 10),and commonly consists of about 6 to 600 continuous filaments (e.g. about20 to 400 continuous filaments). The denier per filament and the numberof continuous filaments present in the yarn may be varied widely as willbe apparent to those skilled in the art.

[0023] The multifilament yarn is particularly suited for use inindustrial applications wherein high strength polyester fibers have beenutilized in the prior art. The yarn of this invention is particularlysuitable for use as tire cord for the reinforcment of tires and for thefiber reinforcement of rubber articles and other composite structures.The fibers are particularly suited for use in environments whereelevated temperatures (e.g. 80° C. to 180° C.) are encountered. Not onlydoes the filamentary material undergo a relatively low degree ofshrinkage for a high strength fibrous material, but it provides enhancedtranslational efficiency for tenacity when the yarn is translated intotreated cord.

[0024] The unexpected combination of tenacity and dimensional stabilityseems to originate from the emergence of a two-phase structure (crystalplus amorphous) during spinning. As a threshold amorphous orientation isachieved there is a simultaneous crystallization of the more orientedamorphous regions.

[0025] In the conventional PET yarn process, crystallization occursmainly in the drawing step since orientation in the spinning column islow. In current commercial dimensionally stable yarn processes, there issignificant amorphous orientation during spinning but crystallizationessentially occurs only in the drawing step. In the present invention,the amorphous orientation in spinning is sufficient to result in modestlevels of oriented crystalline nuclei (with a degree of 3 to 15percent). The consequence of this crystalline nucleation is to removethe high end of amorphous-orientation distribution leaving behind theless oriented amorphous regions. Thus, while the overall orientationincreases with increased spinning stress, the amorphous orientationdecreases immediately following the onset of crystallization in thespin-line. Further increasing the spin-line stress results in more netorientation and more separation of the more oriented amorphous regionsvia crystallization. The net result is further increased amorphousorientation at very high spinning stresses. In such a process amorphousorientation first increases with spinning stress prior to thresholdvalues where crystallization occurs, then decreases as modest spuncrystallinity is achieved, and finally again increases at very highstress levels. The theoretical analysis of the consequence ofcrystallization on amorphous-orientation distribution has been discussedby Desai and Abhiraman [J. Polym. Sci., Polym. Letters Edition, 23,213-217 (1985)].

[0026] The characterization parameters referred to herein mayconveniently be determined by testing the multifilament yarn whichconsists of substantially parallel filaments.

[0027] Birefringence was determined using a polarizing light microscopeequipped with a Berek compensator and the fraction crystallinity wasdetermined by conventional density measurements. The amorphousorientation function was determined from the following relationship (seeR. J. Samuels, Structured Polymer Properties, New York, John Wiley &Sons).

Δn=Xf _(c) Δn _(c)+(1−X)f _(a) Δn _(a) +Δn _(f)

[0028] where

[0029] Δn=birefringence

[0030] X=fraction crystalline

[0031] f_(c)=crystalline orientation function

[0032] Δn_(c)=intrinsic birefringence of crystal (0.220 for polyethyleneterephthalate)

[0033] f_(a)=amorphous orientation function

[0034] Δn_(a)=intrinsic birefringence of amorphous (0.275 forpolyethylene terephthalate)

[0035] Δn_(f)=form birefringence (negligable for this system)

[0036] Crystal orientations were determined with Herman's orientationfunction employing the average angular azimuthal breadth of the (010)and (100) reflections of the wide angle x-ray diffraction pattern:

f _(c)=½(3 cos²φ−1)

[0037] where, f_(c)=crystal orientation function

[0038] φ=average orientation angle

[0039] Density of the undrawn and drawn yarn is a convenient measure ofpercent crystallinity. Densities of undrawn and drawn yarns weredetermined in n-heptane/carbon tetrachloride density gradient column at23° C. The gradient column was prepared and calibrated according to ASTMD1505-68 with density ranging from 1.30-1.43 g/cm³. Percentcrystallinity was then calculated from${{XTAL}\quad \%} = {\frac{( {\rho_{s} - \rho_{a}} )}{( {\rho_{c} - \rho_{a}} )} \times 100}$

[0040] ρs—measured density of sample in gm/cm³

[0041] ρa—theoretical density of 100% amorphous phase (1.335 gm/cm³)

[0042] ρc—theoretical density of 100% crystalline phase (1.529 gm/cm³)

[0043] While birefringence and crystallinity measurements are effectivefor characterizing the amorphous orientation of drawn yarns, undrawnyarn produced near the transition between oriented-amorphous andoriented-crystalline structures demands a more direct method ofevaluating degree of orientation in the amorphous phase. For this, wideangle X-Ray diffraction patterns were obtained in the transmissiongeometry on a Philips diffractometer with Cu radiation and diffractedbeam monochromator. Several radial scans were obtained at variousazimuthal angles between the equator and the meridian. These scans wereresolved into crystalline and amorphous components through a DuPontcurve resolver (Gaussian lineshape). The azimuthal half-width athalf-height (φ½) for the intensity distribution of amorphous halo wasdetermined by plotting the height of amorphous peak as a function ofazimuthal angle.

[0044] Melting points (M.P.) were determined with a Perkin-ElmerDifferential Scanning Calorimeter (DSC) from the maxima of the endothermresulting from scanning a 2 mg sample at 20° C. per minute. As shown inFIG. 9, M.P. is taken to be the temperature of the highest temperaturepeak of the DSC trace. Melting point elevations cited are defined as thedifference between the specimen melting point (M.P.) and the meltingpoint (M.P.Q.) of a specimen after subsequent rapid liquid nitrogenquenching of an encapsulated DSC sample from the melt. The melting pointof this re-crystallized sample is due to crystals which havecold-crystallized during the melting point test procedure. An alternatemeasure of melting point characteristic (Z) which is a more sensitiveparameter than M.P. for many samples of this invention, is defined asthe height (Hg) of the trace at M.P.Q.+9° C. divided by the sum of theheights at M.P.Q.+4° C. (H₄) and at M.P.Q+19° C. (H₁₉):$Z = \frac{H_{9}}{H_{4} + H_{19}}$

[0045] The Z parameter is an important characteristic for drawn yarnswhich have not received a significant thermal treatment. Such drawnyarns have a percent crystallinity from density measurements of 28% orless. Application of an effective heat treatment to the yarn results inan increase in the measured Z value and crystallinity. However, thisadditional heat treatment does not significantly influence the ultimateproperties of the final treated cord. Thus, the measured Z value can behigher than an intrinsic value Z* which reflects inherent differences inthe subsequently treated cords. This intrinsic Z* can be estimated fromthe measured Z and density for drawn yarns receiving a thermal treatmentby the following empirical relation:

log Z/Z*=0.033(XTAL %−27.2)²

[0046] No correction is made for yarns with 27.2% or less crystallinity.Thus, a drawn yarn with Z=1.8 and crystallinity of 29.5% would haveZ*=1.3, which would be the value of Z if the measurement were made priorto the thermal treatment step. Drawn yarns of the present invention havebeen found to have Z* greater than or equal to 1.3. Effective heattreatment of such yarns have produced dimensionally stable yarns with Zgreater than or equal to 1.7.

[0047] Regardless of which melting point characteristic is used, thedifferences in thermal response provide a direct quantitative measure ofdifferences in internal morphological structure. It is felt that thisunique morphological structure rather than melting point 20 elevationper se gives rise to the desired improved performance.

[0048] Intrinsic viscosity (IV) of the polymer and yarn is a convenientmeasure of the degree of polymerization and molecular weight. IV isdetermined by measurement of relative solution viscosity (

_(r)) of PET sample in a mixture of phenol and tetrachloroethane (60/40by weight) solvents. The relative solution viscosity (

_(r)) is the ratio of the flow time of a PET/solvent solution to theflow time of pure solvent through a standard capillary. Billmeyerapproximation (J. Polym. Sci. 4, 83-86 (1949)) is used to calculate IVaccording to${IV} = {{{1/4}\frac{( {\eta_{r} - 1} )}{C}} + {{3/4}\frac{\ln \quad \eta_{r}}{C}}}$

[0049] where C is concentration in gm/100 ml.

[0050] The tenacity values (i.e. at least 7 grams per denier), comparefavorably with these particular parameters exhibited by commerciallyavailable polyethylene terephthalate tire cord yarns. The tensileproperties referred to herein were determined on yarns conditioned fortwo hours through the utilization of an Instron tensile tester (ModelTM) using a 10-inch gauge length and a strain rate of 120 percent perminute in accordance with ASTM D885. All tensile measurements were madeat room temperature.

[0051] The high strength multifilament yarn of the present inventionpossesses an internal morphology which, for a LASE-5 of 4.5 grams perdenier or greater, manifests an unusually low free shrinkage propensityof less than 8 percent, and preferably less than 6 percent when measuredin air at 177° C. For instance, filaments of commercially availabledimensionally stable tire cord yarns based on polyethylene terephthalatecommonly shrink about 6 to 10 percent when tested in air at 177° C. Freeshrinkage (FS) values were determined in accordance with ASTM D885 withthe exception that the testing load was 9.3 grams. Such improveddimensional stability is of particular importance if the product servesas fibrous reinforcement in a radial tire. Elongation at the specifiedload of 4.5 g/d (E_(4.5)) is an alternate indicator of modulus. It isparticularly useful in that the sum E_(4.5)+FS is a good indicator ofdimensional stability for yarns processed under different relaxationlevels. Lower sums (E_(4.5)+FS) indicate better dimensional stability.

[0052] The Kinetic Theory of Rubber Elasticity allows computation of aneffective number of crosslinks in a yarn. These crosslink values areimagined to be a measure of the ability of the crystals to tie togetherthe amorphous regions, either via tie chains or crystal proximity. Therelationship of interest is:

δ=NkT(A ²−1/A)

[0053] where,

[0054] δ=shrinkage force

[0055] k=Boltzman constant

[0056] T=temperature

[0057] A=extension ratio=1/(1-shrinkage)

[0058] N=network chains or crosslinks/cc

[0059] The classical method for determining crosslink density is tomeasure shrinkage force and shrinkage for samples which have been drawn(or relaxed) to different extents. For simplicity, we have developed amethod which allows one to determine analogous data by measuring theshrinkage at a variety of constraining forces. For this modifiedtechnique, the constraining force corresponds to the shrinkage force.The shrinkage value needed for the effective crosslink calculation isthe difference between the shrinkage measured at a given constrainingforce and the shrinkage measured at a minimal constraining force of 5grams. Note that since curvature is exhibited at high shrinkage forcesonly data up to a shrinkage force of 0.08 kg/d should be used for theabove computation. For industrial applications, a temperature of 1770°C. was employed

[0060] Identified hereafter is a description of a process which has beenfound to be capable of forming the improved yarn of the presentinvention. The yarn product claimed hereafter is not to be limited bythe parameters of the process which follows.

[0061] The melt-spinnable polyester is supplied to an extrusionspinnerette at a temperature above its melting point and below thetemperature at which the polymer degrades substantially. The residencetime at this stage is kept to a minimum and the temperature should notrise above 315° C., preferably 310° C. The flow curve of molten PET interms of melt viscosity versus shear rate has been shown to be importantfor steady-state melt spinning giving uniform individual multifilaments.For a circular spinnerette hole where flow is steady and end-effects arenegligible, the apparent shear rate ({dot over (γ)}) at the wall of thecapillary is given by$\overset{.}{\gamma} = \frac{4Q}{\pi \quad R^{3}}$

[0062] where

[0063] Q=flow rate through the capillary in m³/sec (calculate using meltdensity of 1.30 g/cc)

[0064] R=radius of the capillary in meters.

[0065] The extruded filaments then traverse a conventional yarnsolidification zone where quench air impinges on the spun yarn therebyfreezing in desirable internal structural features and preventing thefilaments from fusing to one another. The solidification zone comprises(a) a retarded cooling zone, preferably comprising a gaseous atmosphereheated at a temperature of 150 to 450° C., and (b) a cooling zoneadjacent said retarded cooling zone wherein said yarn is rapidly cooledand solidified in a blown air atmosphere. The key to the current processis to utilize extruding polymer with IV greater than 0.80 and adjustprocessing conditions to achieve a crystalline, partially oriented yarnwith a crystallinity of 3 to 15 percent and a melting point elevation of2 to 10° C. One skilled in the art can achieve this by adjusting thefollowing conditions: length and temperature of an annealing zoneadjacent to the spinnerette, diameter of the spinnerette holes, methodof blowing the quench, quench air velocity, and drawdown in the quenchcolumn. The speed of withdrawal of the yarn from the solidification zoneis an important parameter affecting the stress on the spun fiber, andshould be adjusted to yield the desired characteristics. It is preferredthat the melting point elevation be 2 to 5° C. and that φ½ is at least26°.

[0066] The spun yarn was then drawn between rolls at temperatures abovethe glass transition temperature (80° C.) to within 85 percent of themaximum draw ratio. This drawing process involves multiple drawing andconditioning steps to achieve a tenacity above 7 grams per denier, aLASE-5 above 3.7 grams per denier and a shrinkage less than 8 percent.It is preferred that the effective crosslink density (N) be between10×10²¹ and 20×10²¹ crosslinks per cubic centimeter.

[0067] It will be appreciated by those of skill in the art that the highviscosity polymer spun as above can be drawn in known ways such as thatdisclosed in U.S. Pat. No. 4,195,052 to Davis et al. and in U.S. Pat.No. 4,251,481 to Hamlyn. The yarn can be drawn off-line. However, foreconomic reasons it is preferred to draw the yarn in a continuousintegrated spin-draw process.

[0068] The drawn yarns are usually twisted into a cord and then dippedinto one or more conventional adhesive coatings, referred to as corddips and then subjected to various stretch/relax sequences at elevatedtemperature to 5 achieve the optimum combination of tenacity, shrinkage,LASE-5. Again this technology is well-known to those skilled in the artwho adjust twist and treating conditions for specific end-uses. Detailsfor the treating conditions employed are given in the examples.

[0069] In evaluating the potential of tire yarns as treated cords, onemay use a “standard” twist and cord treatment for comparative purposes.In this “standard” procedure, 1000 denier yarns are twisted to 8 turnsper inch and then three ply cords are prepared again using 8 turns perinch. The cords are then dipped in an aqueous blocked diisocyanate (6%solids) just prior to passage through a hot air oven at 440° F. for 40seconds where the cord was stretched 6% or 8%. The emerging cord thenpasses through an RFL dip (20% solids) and finally through a second ovenat 440° F. for 60 seconds where the cord was relaxed to varying degreesto cover the range where 4% free shrinkage is achieved. For lessdimensionally stable cord controls, some extrapolation to 4% shrinkagemay be necessary. The cord is wound on a bobbin for further testing. Asingle-end Litzler Computreater was used.

[0070] Treated cords prepared in such manner from the yarn of thisinvention have been shown to have the following treated cord properties:

[0071] (a) a dimensional stability defined by LASE-5 of at least 2.3grams per denier at 4 percent free shrinkage, and

[0072] (b) a tenacity of at least 7.0 grams-per denier at 4 percent freeshrinkage (preferred at least 7.4 grams Dper denier), said dimensionalstability and said tenacity being determined by interpolation of LASE-5versus free shrinkage data to 4 percent free shrinkage.

[0073] Graphs of LASE-5 and tenacity versus free shrinkage wereconstructed as shown in FIGS. 1-4. Comparison between different startingyarns can be made at the interpolated values at 4% free shrinkage.

EXAMPLE I

[0074] A 1000 denier PET yarn was produced by extruding 300 individualfilaments at 62.5 lbs/hr into a heated sleeve (220-300° C. Temp) andthen solidifying in an air quenching column. Yarns were then taken-up atvarying winder speeds. The residence times in the heated sleeve andquench columns were 0.02 to 0.03 and 0.2 seconds, respectively. TheGodet speed at the bottom of the spinning column and the winder speedwere adjusted to give different undrawn birefringences and crystallinitylevels. In all cases the same shear rate in the spinnerette holes wasemployed. Yarn intrinsic viscosity was 0.88.

[0075] These undrawn yarns were then drawn in three stages on adraw-winder. The first three godet rolls had temperatures of 120, 120,and 230° C., the last godet was ambient. The residence times were 0.7,0.6-0.7, 0.3-0.6, and, 0.2-0.4 seconds. Yarn draw ratios and specificproperties are given in Tables I and II.

[0076] The above drawn yarns were then twisted into 1000/3, 8.5×8.5 tpicords and two-zone treated at 440° F. (227° C.) and 440° F. (227° C.)for 40 and 60 seconds. Aqueous blocked diisocyanate and RFL dips wereapplied prior to the two hot zones, respectively. The treated cords wereprepared using +6% stretch in the first zone and various relaxations(−4, −2, and 0%) in the second zone. A stretching sequence of +8, 0% wasalso used. The properties of these cords are given in Table III. Treatedcord dimensional stabilities, as judged by plots of LASE-5 versus freeshrink (FIG. 1), increase with increasing undrawn yarn birefringence,melting point, and crystallinity.

[0077] Comparison of the treated cord tenacities at a given freeshrinkage (FIG. 2) clearly indicates an unexpected high tenacity for theundrawn intermediate birefringence of 0.056. This higher treated cordtenacity is equal to that for standard tire yarn processed at very lowundrawn birefringence. While drawn yarn tenacitites alone are notnecessarily a good barometer for treated cord tenacity, the combinationof yarn tenacity and dimensional stability (E_(4.5)+FS) does give a goodindication, provided similar thermal histories are experienced duringdrawing. For the samples representing this invention (I-BD and I-CD),E_(4.5)+FS is 10.2% and 10.1% respectively, indicating highlydimensionally stable yarns. These sums would have been slightly higher(2-3%) if the yarn 10 was drawn at higher speeds where residence timeson heated rolls were lower. Note the melting points (258° C. and 259°C.) lies between that for comparative examples I-AD and I-DD. Note thatthe spinning speed required to achieve the 0.056 undrawn birefringenceis less than that for the prior art in FIG. 8.

[0078] The yarns of this invention, I-BD and -CD, have high measuredvalues of Z. Their cord dimensional stabilities are similar as are theircalculated Z* values, which take differences in crystallinities intoaccount.

EXAMPLE II

[0079] A higher viscosity yarn (IV=0.92) was spun under similarconditions as in Example I except that several spinnerette shear rateswere used. Following the same procedure as in Example I, the winderspeed was adjusted to provide different undrawn crystallinities. Thisundrawn yarn was continuously transported to the panel draw rolls.Details for the undrawn and drawn yarns are given in Tables IV and V.The residence times on the draw rolls was 0.05 to 0.1 second and thegodet temperatures were 90° C., ambient, 220° C. and 150° C. Forcomparison, values for a conventional yarn spun to 0.002 undrawnbirefringence are also given. From FIG. 7 it is readily seen that theproducts of this invention (II-B and II-C) are prepared in thetransition region where significant crystallinity 30 occurs in thespinline. The effective number of crosslinks in Table V is calculatedfrom the shrinkage versus shrink force curves in FIG. 10.

[0080] The preceeding drawn yarns were twisted into a 1000/3, 8×8 tpicord and then treated per Example I. Again 35 treated cord dimensionalstability (Table VI and FIG. 3) increased with undrawn crystallinity.However as shown in FIG. 4, the highest tenacity was achieved atintermediate LASE-5. The corresponding drawn yarns have tenacity greaterthan 7.3 g/d, E_(4.5)+FS less than 12.9%, intermediate meltingpoints(259 and 262° C.), low amorphous orientation, and a melting traceintensity parameter (Z*) of at least 1.3. The actual DSC traces aregiven in FIG. 9. When slight differences in twist are taken intoaccount, the dimensional stability of II-BD is similar to I-BD and -CD.The measured Z is much lower than those for Example I, which have highercrystallinity due to lower viscosity and slower drawing stages. Due tothe high drawing speeds and modest roll temperatures, none of thesamples in this example received an effective heat treatment. Themaximum crystallinity without heat treatment is 27-28% with 27.2%representing the average.

[0081] LASE-5 versus free shrink can be used as an alternate measure ofdrawn yarn dimensional stability. FIG. 5 gives such a plot for drawnyarns prepared similar to II-AD and II-ED, but then relaxed to variousdegrees in the final zone. The solid lines in FIG. 5 represent the datafor the relaxation series where (x) and (o) represent points for yarnssimilar to II-AD and II-ED, respectively. The individual data pointsfrom Table IV are also plotted as encircled sample designations fromTable IV. One would expect a family of linear lines with increasingslope. On this basis, the products of this invention would be defined by

LASE-5(g/d)>0.35 [Free Shrink (%)]+1.0.

[0082] The advantages of this patent are more clearly shown by FIG. 6which plots tenacity versus LASE-5 at a given free shrinkage (4%). Basedon the decrease in tenacity in-going from conventional yarn (undrawnΔN=0.002) to prior art DSP's (undrawn ΔN=0.026), one would expect thecontinual decrease in treated cord tenacity with increasing LASE-5,particularly in light of the low tenacity at very high undrawnΔN(=0.082). Instead one sees an unexpected maximum at intermediateLASE-5. Again note that the spinning speeds required are much less thanthose taught in U.S. Pat. No. 4,491,657. This lower speed allowspreparation of fibers in a continuous spin-draw process without the needfor expensive high speed equipment.

EXAMPLE III

[0083] This example shows that yarn tenacity and dimensional stabilityOre not sufficient criteria to define the product of this invention.Yarns spun to 0.002 and 0.026 undrawn birefringences were then drawn inthe manner described in Example II. They were then given heat treatmentsof either (a) 6 seconds @ 245° C. or (b) several hours @ 210° C. atconstant length. Subsequently, the yarn was corded (1000/3, 8.5×8.5) andtreated per Example I. The data in Table VII shows that additionalparameters of melting point elevations and amorphous orientations arenecessary to specify yarns of this invention. The lower amorphousorientation yarns of this invention are expected to have longerflex-life.

EXAMPLE IV

[0084] This example shows that one must focus on fundamental propertiessuch as undrawn yarn crystallinity and melting point elevation and noton undrawn birefringence alone. A yarn series was processed undersimilar conditions to Example I, only the thruput was 75 lbs/hr, theheated sleeve was 400° C., and the spinnerette shear rate was 766 sec⁻¹.At 0.058 undrawn birefringence, the drawn yarntenacity/UE/LASE-5/FS/E_(4.5)+FS was 8.1/9.9/4.1/8.6/14.8. At 0.081undrawn birefringence, the drawn yarn was 8.0/9.5/4.1/7.5/11.9. The twodrawn yarns had melting point elevations of 8 and 13° C., respectively.Under the standard treating conditions, the tenacity and LASE-5 valuesat 4% FS were 6.7 g/d and 2.2 g/d for the 0.058 undrawn birefringencecompared to 7.1 g/d and 2.6 g/d for the 0.081 undrawn birefringenceyarn. Only the latter product was within the scope of this inventioneven though the undrawn birefringence for the former was similar to thatfor I-BD and I-CD, which are within the scope of this invention. TABLE IUNDRAWN YARN (IV = 0.88) Spinning Spinnerette Speed Shear Rate, M.P.,Density, XTAL, Example m/min Sec⁻¹ ΔN ° C. ΔM.P. g/cm³ % I-A 1760 21500.028 250 1 1.3385 2 I-B,I-C 2900 2150 0.056 252 3 1.3480 4 I-D 35002150 0.088 261 12  1.3701 18 

[0085] TABLE IV UNDRAWN YARN (IV = 0.92) Spinning Spinnerette SpeedShear Rate, M.P., Density, XTAL, φ_(½) Example m/min Sec⁻¹ ΔN ° C. Δm.p.g/cm³ % (deg) II-A 1760 2150  0.026 249 0 1.3430 3 21 II-B 2020 9100.055 252 3 1.3494 7 32 II-C 2420 980 0.069 253 4 1.3603 13  — II-D 2990640 0.082 265 16  1.3707 18  19 II-E  480 1440  0.002 249 0 1.3385 2 —

[0086] TABLE II DRAWN YARN (IV = 0.88) Tena- Terminal E_(4.5), DrawRatio city LASE-5 E_(4.5) Mod. UE, FS(%), +FS, M.P., Example^(a) 1 2 3Denier g/d g/d % g/d % @177° C. % ° C. ΔM.P.^(b) Fa Z Z* XTAL% I-AD 1.721.38 1.03 1016  7.8 4.1 5.2 128 9.8 9.0 14.2 257  8 0.73 0.4 0.3 29.3I-BD 1.72 1.10 1.04 898 7.8 5.4 4.1 111 7.2 6.1 10.2 258  9 0.71 2.5 1.530.2 I-CD 1.72 1.10 0.98 943 7.0 4.0 4.6  54 8.9 5.5 10.1 259 10 0.701.7 1.4 29.2 I-DD 1.40 1.10 1.05 799 6.5 5.8 3.2  78 6.2 4.7 7.9 267 180.68 0.6 0.2 31.4

[0087] TABLE III TREATED CORD PROPERTIES (IV = 0.88) FS (%), Tenacity,LASE-5, at UE, Toughness Example^(a) Stretch g/d g/d 177° C. % g/d I-AT+6/−4 6.0 2.48 4.8 11.7 0.34 +6/−2 6.0 2.62 5.4 11.5 0.34 +6/−0 6.0 3.016.7 10.1 0.30 +8/−0 6.0 2.95 7.0 9.7 0.29 I-BT +6/−4 6.6 2.70 4.2 13.60.50 +6/−2 6.7 3.34 6.3 11.6 0.44 +6/−0 6.7 3.46 6.7 10.6 0.38 +8/−0 7.03.50 6.8 11.0 0.42 I-CT +6/−4 6.3 2.20 2.6 16.1 0.59 +6/−2 6.3 2.64 3.714.4 0.53 +6/−0 6.5 2.99 4.6 13.3 0.50 +8/−0 6.4 3.08 4.8 13.3 0.51 I-DT+6/−4 5.8 3.77 3.3 10.2 0.36 +6/−2 5.6 3.58 3.2 11.2 0.39 +6/−0 5.6 3.873.9 10.9 0.39 +8/−0 6.0 4.00 4.1 9.1 0.31

[0088] TABLE V DRAWN YARN (IV = 0.92) Tena- Terminal Draw Ratio cityLase-5 Modulus Example^(a) 1 2 3 Denier g/d g/d g/d II-AD 1.73 1.46 0.981008 8.1 3.9 95 II-BD 1.73 1.25 0.99 1007 8.1 4.0 128  II-CD 1.73 1.161.00  982 7.3 3.9 — II-DD 1.40 1.15 1.00  924 5.8 4.1 78 II-ED — — —1005 9.3 3.1 — Free E_(4.5), UE, Shrink, E_(4.5), M.P., Example^(a) % %@177° C. +FS, % ° C. ΔM.P.^(b) II-AD 5.5 10.0 10.0 15.5 256  7 II-BD 5.59.9 7.4 12.9 258 10 II-CD 5.7 10.0 5.8 11.5 259 10 II-DD 6.5 16.5 4.310.8 269 20 II-ED 6.9 15.3 10.8 17.7 255  6 Example^(a) Z Z* Fa XTAL%N^(c) II-AD 0.7 0.7 0.70 27.5  8.4 II-BD 1.5 1.5 0.66 26.6 11.6 II-CD1.3 1.3 0.64 27.6 — II-DD 0.3 0.3 0.58 28.7 26.6 II-ED <0.1 — 0.87 — —

[0089] TABLE VI TREATED CORD PROPERTIES (IV = 0.92) FS (%), Tough-Tenacity, LASE-5, at UE, ness, Example Stretch g/d g/d 177° C. % g/dII-AT +1/−0 6.7 2.43 4.9 15.0 0.50 +6/−4 6.9 2.50 5.1 13.7 0.47 +6/−27.0 2.80 6.9 11.5 0.40 +6/−0 7.3 3.08 7.3 11.1 0.41 +8/−0 7.3 3.24 7.811.0 0.40 II-BT +1/−0 7.1 2.41 3.2 16.4 0.62 +6/−4 7.2 2.55 3.2 16.10.61 +6/−2 7.6 3.20 4.7 14.9 0.60 +6/−0 7.7 3.39 5.9 13.3 0.56 +8/−0 7.73.37 6.3 12.6 0.53 II-CT +1/−0 6.6 2.40 2.9 16.3 0.61 +6/−4 6.8 2.73 2.916.1 0.62 +6/−2 7.0 3.16 5.0 13.9 0.57 +6/−0 7.1 3.24 5.4 13.0 0.50+8/−0 7.1 3.36 5.8 12.6 0.50 II-DT +1/−0 4.9 2.50 1.8 18.9 0.66 +6/−45.2 2.56 1.9 18.5 0.64 +6/−2 5.3 3.14 3.2 16.9 0.64 +6/−0 5.4 3.53 3.915.2 0.59 +8/−0 5.6 3.60 4.0 14.1 0.53 II-ET +1/−2 7.3 2.4 7.3 16.9 0.64+6/−4 7.0 2.2 6.8 17.5 0.62 +6/−2 7.4 2.9 8.9 14.8 0.59 +6/−0 7.4 3.310.2 13.2 0.54

[0090] TABLE VII Yarn Treated Cord Undrawn Yarn Heat Tenacity, E_(4.5)M.P., Tenacity, g/d LASE-5, g/d Birefringence Treatment g/d +FS, % ° C.Fa @ 4% FS @ 4% FS 0.002 None 8.9 16.8 255 0.87 6.9 1.2 6 sec @ 245° C.8.9 11.0 — 0.83 — — 8 hr @ 210° C. 7.5 7.2 — 0.90 6.0 2.5 0.026 None 8.013.8 256 0.70 6.6 2.5 6 sec @ 245° C. 7.9 8.0 256 0.63 6.6 2.5 2 hr @210° C. 8.0 7.0 254 0.67 6.3 2.8 0.056 None 8.1 12.5 258 0.66 6.9 2.8

What is claimed is:
 1. A process for production of a drawn polyethyleneterephthalate yarn which translates to a high tenacity dimensionallystable tire cord, comprising: (A) extruding a molten melt-spinnablepolyethylene terephthalate having an intrinsic viscosity of 0.8 ofgreater through a shaped extrusion orifice having a plurality ofopenings to form a molten spun yarn, (B) solidifying the spun yarngradually by passing the yarn through a solidification zone whichcomprises (a) a retarded cooling zone and (b) a cooling zone adjacentsaid retarded cooling zone wherein said yarn is rapidly cooled andsolidified in a blown air atmosphere, (C) withdrawing the solidifiedyarn at sufficient speed to form a crystalline, partially oriented yarnwith a crystallinity of 3 to 15% and a melting point elevation of 2 to10° C., and (D) hot drawing the yarn to a total draw ratio between 1.5/1and 2.5/1.
 2. The process of claim 1 wherein the melting point elevationis 2 to 5° C.
 3. The process of claim 1 wherein φ½ is at least 26°. 4.The process of claim 1 wherein the steps A, B, C, and D are performed ina continuous integrated spin-draw process.
 5. The process of claim 4wherein the melting point elevation is 2 to 5° C.
 6. The process ofclaim 4 wherein φ½ is at least 26°.
 7. A drawn polyethyleneterephthalate multifilament yarn having the following combination ofproperties: (A) a terminal modulus of at least 20 g/d, (B) a dimensionalstability defined by E_(4.5)+FS<13.5%, (C) a tenacity of at least 7grams denier, (D) a melting point elevation of 9 to 14° C., and (E) anamorphous orientation function of less than 0.75.
 8. The drawn yarn ofclaim 7 wherein the melting point elevation is 9-11° C.
 9. The drawnyarn of claim 7 which has the melting point characteristic defined by Z*greater than or equal to 1.3.
 10. Dimensionally stable yarns of claim 7which have the melting characteristic defined by Z greater than or equalto 1.7.
 11. The drawn yarn of claim 7 which has an effective crosslinkdensity (N) between 10×10²¹ and 20×10²¹ crosslinks per cubic centimeter.12. A high tenacity, dimensionally stable treated tire cord preparedfrom the yarn of claim
 7. 13. A rubber article incorporating asreinforcing material the high tenacity, dimensionally stable cord ofclaim
 12. 14. A composite incorporating as reinforcing material thedrawn yarn of claim
 7. 15. A drawn polyethylene terephthalate yarnwhich, when twisted into an 8×8 twists per inch 1000 denier 3-end greigecord and tensilized by the sequence of dipping into a first blockeddiisocyanate dipping solution, stretching at 440° F. (227° C.) for 40seconds, dipping into a second resourcinol-formaldehyde-latex dippingsolution, and relaxing at 440° F. (227° C.) for 60 seconds, provides thefollowing treated cord property combinations: (a) a dimensionalstability defined by LASE-5 of at least 2.3 grams per denier at 4percent free shrinkage, and (b) a tenacity of at least 7.0 grams perdenier at 4 percent free shrinkage, said dimensional stability and saidtenacity being determined by interpolation of LASE-5 versus freeshrinkage data to 4 percent free shrinkage.
 16. The yarn of claim 15which provides a treated cord tenacity of at least 7.4 grams per denier.